Battery packs housing secondary batteries are commonly used to power cordless power tools (For example, refer to Japanese Patent Application Publication No. 2011-136405). A power tool includes a motor that produces an output suited to the application of the power tool, and a control circuit configured of a field-effect transistor (FET), for example, that controls the electric current supplied to the motor. Conventionally, power tools have been provided with a specialized battery pack having a voltage and capacity suited to the output of the motor and FET. As a result, a plurality of types of battery packs exists for a plurality of types of power tools.